1. Related Applications
This invention is related to U.S. patent application, Ser. No. 391,043, filed June 22, 1982, now abandoned, and to U.S. Pat. No. 4,350,093.
2. Field of the Invention
The present invention relates to a picture image adjusting device in a sheet-feed offset press.
3. Background of the Invention
When four-color printing is performed on a sheet-feed offset press, it is conventionally necessary to make each of first-color and second-color pictures register with the paper before the first-color and second-color pictures are made to register with each other. Then, it is necessary to make each of third-color and fourth-color pictures register with the paper on which the first-color and second-color pictures have been printed when the third-color and fourth color pictures are to be printed on the paper. If there is an error in plate making, torsion in plate attachment, or the like, the above-mentioned color pictures are not coincident with each other thus causing color slip, resulting in obscure printing.
There are conventional devices in which the slanting of a picture due to distortion in a plate or an error in picture registration between colors can be corrected. An example of such a device is disclosed in Japanese Utility Model Unexamined Publication No. 61940/1984. In this device, a previous guess is made with respect to an impression cylinder and slanting of the picture is adjusted. In the device disclosed in Japanese Utility Model Publication No. 19921/1976, a plate cylinder is distorted.
In the former device, however, there are problems in that the adjustment cannot be performed during operation of the press and in that the manufacturing cost is high because of its complicated structure.
In the latter device, on the other hand, there are problems that because the slant picture adjustment is performed by distorting the plate cylinder, the roller pressure and the plate pressure are finely changed so as to cause a difference in printing pressure of the roller between the central portion and its end portion to thereby cause unevenness in printing.